New Breakdown Calculation Method for Gas-insulated High Voltage Applications

This contribution is focused on a new calculation method of the breakdown voltage i.e. the dielectric strength of gases in dependence of pressure, distance and arbitrary electrode and electric field arrangement, within the weakly inhomogeneous electric field. This breakdown voltage calculation is based on the well-known criterion according Townsend and Raether with the theory of charge carrier multiplication by impact ionization. The enhancement of these theories is the iterative calculation of the streamer propagation in gases with a superimposed electric field strength in addition to the background field. Furthermore, the model of the streamer gets enhanced by Paschen's gas parameter A to achieve a dependence on pressure. This new breakdown voltage calculation algorithm requires the distribution of the electric field along its critical breakdown path, e.g. from a FEM simulation. The algorithm is based on a huge database of breakdown measurements of SF6, synthetic air, N2, CO2 with a variation of pressure and sparking distance $({p}=\mathbf{0.1}\ldots \mathbf{2.6\ MPa},\ {d}=\mathbf{0.5}\ldots \mathbf{45\ mm})$ at AC and DC voltages up to 300 kV and LI voltages up to 750 kV. According to this new algorithm a mathematical term is extracted which combines the theories of Schwaiger and Paschen to simplify calculations when FEM field simulation is done. For this a new notion of the ignition field strength $\overline{E}_{\mathrm{i}}$ is introduced. This method improves and simplifies breakdown calculations in gases by reducing the time effort. A verification of this calculation methods was done by measurements in laboratory measurements up to 750 kV and 2.6 MPa.